It is often desirable to run a casing jet perforating gun downhole and to perforate a casing with a very close distribution of perforations. In the past, this has been achieved by running a select fire gun downhole and repositioning the gun between each shot and consequently, the distribution pattern of the shaped charges is speculative for the reason that the exact orientation of the gun between shots is unknown and therefore, it is possible to place all of the perforations through the same hole formed in the casing, and of course, this is a very undesirable perforating job. Moreover, it is possible to inadvertently space the shots in a pattern which damages the casing or which causes jagged edges thereof to be formed which presents difficulty in subsequently running tool strings downhole.
Others have resorted to using a jet perforating gun having single charges spaced apart from one another on a very wide spacing and by making several expensive trips into the hole so that the resultant number of desired perforations can be achieved, however, here again the distribution of the shots is questionable for the obvious reason that orientation of the gun and the slight difference in elevation between trips inherently provides a large margin of error.
It would be desirable to be able to arrange a plurality of shaped charges within a perforating gun in such a manner that a high density pattern of symmetrical perforations may be achieved in a single firing of the gun with as many as 12-20 perforations per foot being realized. Such a desirable expedient would provide a perforated casing with a definite distribution pattern which has heretofore been unavailable. Such a desirable expedient is the subject of this invention.